Effect of Aggregation on the Respiration Rate of the Freshwater Unionid Bivalve, Elliptio complanata (Solander)

The freshwater unionid bivalve, Elliptio complanata (Solander), has an aggregated distribution in Morice Lake, New Brunswick, Canada. Respiration rate, as measured in a 23 liter respirometer under varying degrees of aggregation, showed a significant decline as the number of bivalves was increased from 1 to 7 and then remained constant. Preliminary experiments suggest that a single individual uses oxygen at the same rate as each individual in a larger group when placed in water previously containing the larger group. It is hypothesized that the presence of other individuals in the vicinity in some way makes each individual more 'comfortable' and consequently lowers the extent to which water is transported to sense the environment which in turn reduces respiration rate.